Photothermal-stable pure-iodide wide-bandgap perovskite solar cells with suppressed ionic losses

Abstract

Mixed-halide wide-bandgap (WBG) perovskites are commonly used for Si/perovskite tandem solar cells; however, their operational stability remains limited by halide segregation, greatly constraining the operational device lifetime. Recent research efforts have turned towards pure-iodide alternatives, which do not undergo halide segregation despite somewhat larger open-circuit voltage (V_OC) deficits. However, their potential to withstand harsh photothermal stressors (e.g., light + 85 °C heat), which is a crucial step towards an operational lifetime of 25 years, remains underexplored. Here, we present an optimized mixed-cation, dimethylammonium (DMA)-stabilized, pure-iodide Cs_0.3DMA_0.2MA_0.5PbI₃ WBG cell (E_g: ∼1.68 eV), with a V_OC of up to 1.25 V and the highest certified efficiency (>22%) for this system, achieved through a dual-layer passivation strategy. In contrast to the mixed-halide system, the pure-iodide composition maintains a stable emission yield and demonstrates remarkable resilience to the evolution of ionic losses and ion density under illumination and thermal aging. This results in negligible degradation during the maximum power point tracking at 40 °C and the longest reported projected T80 lifetime (8140 h) for WBG (∼1.65–1.73 eV) perovskites under 85 °C photothermal stress (ISOS-L-2). Our work provides a mechanistic basis for the exceptional stability of pure-iodide WBG perovskites and outlines a viable pathway toward highly efficient and durable perovskite tandem solar cells.